Flexor-reflex evoked by a Single BreaJc-shock. Ill 



seemingly even lower than can be accounted for wholly by the impaired 

 state of the peripheral nerve-muscle apparatus itself. The wasting of the 

 limb-musculature is also very obvious. The condition was clearly less 

 favourable for the observations we had in view than that obtaining in the 

 earlier periods after the transection. 



Discussion of Results. — 1. In the assemblage of striped fibres composing a 

 muscle, the modes of summation of their contraction are of course two. One 

 of these is that exemplified in the twitch contraction. There, in each of 

 some or all of the component fibres of the muscle, a single wave of con- 

 traction is generated ; the occurrence of this wave is practically simultaneous 

 in all the contracting fibres. These individual mechanical tensions of the 

 several component fibres of the muscle sum additively ; the tension 

 developed by the muscle, as a whole, gives the resultant tension of this 

 single-wave contraction. The upper limit of the tension-efiect of this 

 summation of a single-wave contraction, coincident in time in the indi- 

 vidual fibres of the muscle, can be found for a given muscle from the 

 isometric record of its maximal twitch. Where the given muscle develops a 

 tension superior to that developed in its maximal twitch, there must be at 

 play, above and beyond summation of the above kind, some amount of that 

 other well-known mode of summation due to fusion of successive contraction- 

 waves ensuing within the self-same individual fibres of the muscle. We may 

 for brevity distinguish these two kinds of summation as " fibre summation " 

 and " wave summation " respectively. 



Applying this to the above-mentioned result, namely, to the excess of 

 crest-height observed in the reflex contraction as contrasted with the 

 maximal twitch when the former is excited by a break-shock of considerably 

 above threshold value, yet not greater than that used for the compared 

 maximal twitch, we infer that there is in the reflex contraction a factor of 

 wave-summation in addition to the fibre-summation. That is, a single 

 break-shock stimulus, which evokes in the neuromyal preparation a single 

 wave contraction, evokes when applied to the afferent nerve a succession of 

 contraction waves, at least in some of the fibres of the muscle. 



2. A possible reason for this might be that a proprioceptive reflex, initiated 

 by the contracting muscle itself, appended itself to the reflex contraction 

 evoked by the extrinsic afferent nerve. In the spinal preparation, a proprio- 

 ceptive reflex is easily elicited from tibialis an tic us (Asayama) (1), e.g., by a 

 brief pluck upon the severed tendon of the muscle. We therefore proceeded 

 to observations in which the afferent nerve-fibres from the muscle had been 

 severed from their connections with the spinal cord. The afferent nerve- 

 fibres from tibialis anticus, and, indeed, from all the pre-tibial and post- 



